This invention relates, in general, to a process for enhancing the rate of removal of water from surface during the evacuation cycle prior to processing semiconductor devices and, more particularly, to the addition of a volatile organo chlorosilane prior to the deposition of metallic films on semiconductor device wafers.
Chemical and physical deposition processes such as chemical vapor deposition, low pressure chemical vapor deposition, plasma enhanced chemical vapor deposition, sputtering and E-beam evaporation are utilized for the formation of various thin films. Many of these films are essential in the fabrication of semiconductor devices. Among these are semiconductor materials such as: epitaxial and polycrystalline silicon; dielectric marerials such as silicon oxide and silicon nitride; and metallic materials such as aluminum, gold, and tungsten. More recently, interest in the deposition of advance refractory metallic films such as selective tungsten, tungsten silicide, titanium silicide, titanium nitride, and titanium boride have been used. As applied to the electronics industry, these refractory metallic films are used as: improved gate electrodes and interconnections on MOS devices; contact enhancements to semiconductor materials; metallization of Schottky devices; diffusion barriers; and the like.
Typically, the properties of a thin film are attributed to a combination of the bulk film properties and surface and/or interface effects. Bulk film properties are attributed to the intrinsic properties of the material modified by factors such as chemical composition (and stoichiometry), impurities levels in crystallinity. These bulk film properties include: interface properties which include mechanical properties such as adhesion and stress; physical properties which include crystallinity and defects; electrical properties including contact resistance and conductivity; and chemical properties such as impurity content, stoichiometry and deposition, and etching selectivity. Furthermore, as the film thickness is reduced the surface/interface effects are even more prominent. The interfaces are strongly influenced by surface cleanliness and ambient environment within the deposition reactor at the initiation of the deposition cycle. The major contaminant on nearly all surfaces is water. The source of the water is moisture in the environment and wet chemical processing techniques. Water continues to bond to surfaces even under vacuum because of the strong bonding interaction between the polar water molecules and surfaces.
In addition, "hydrogen bonding" between layers of water molecules accounts for adhesion of water films tens of molecules thick. Prior to the deposition of a film, in an evacuated environment, the atmosphere in the deposition system is removed by mechanical pumping to a pressure between about 0.01 to 0.001 torr. This atmosphere is usually deemed adequate for low pressure chemical vapor deposition applications. Physical deposition systems such as sputter and e-beam evaporation require additional high vacuum pumping (e.g. diffusion pump cryogenic pump) to render pressures less than 10.sup.- 5 torr. In both low pressure chemical and physical deposition reactors a major constituent of the residual atmosphere during final pump down is water vapor which is slowly released from the deposition surface and walls of the reactor. Evacuation alone will not remove all of the water from the surfaces without additional techniques, such as heating and/or carrier gas purge.
At the initiation of the deposition cycle, water on the deposition surface and a portion of the water in the reactor come in direct contact with the materials being deposited and in many instances react with these materials as they are being deposited. In the case of metallic source materials, these reactions generally produce a metallic oxide. These water related impurities are concentrated at the interface and make it difficult to etch or deposit with high selectivity. The water related impurities: impair adhesion and electrical contact; add to the stress of many films; and, in general, result in a multitude of processing reliability problems.
An additional problem is encountered in reducing the effects of residual water vapor in a low pressure chemical vapor deposition system or in a plasma enhanced chemical vapor deposition system. Metallic source materials are typically halides of the metal being deposited. These halides are highly reactive with water and form oily residues which adhere to surfaces and further react with water on exposure to the ambient. These types of residues readily clog small orifices like those found in mass flow controllers, check valves, and injectors. Accordingly, the metallic source materials mass flow controllers require substantial maintenance especially after the system has been open to the ambient.
A further problem that should be considered is that of moisture in the vacuum pump oil. During the evacuation cycle, prior to deposition, the pump oil is subjected to increasing concentrations of water vapor. Purging with an inert ambient significantly helps to flush out the water vapor. However, at the completion of the purge cycle, the water level rises again. This water vapor markedly reduces the effective pumping speed especially at reduced pressures. Furthermore, at the initiation of deposition, the metallic source materials react with the water in the pump oil and leave residues which can potentially reduce the life of the oil and pump.
Although some of the foregoing problems can be overcome by using a refractory metal LPCVD reactor, in which all internal surfaces can be heated and flushed before each deposition, these modifications increase the complexity of the reactor and still result in varying quantities of residual water on the surface. Furthermore, problems with mass flow controller reliability and water in the vacuum train remain.
Accordingly, a need has existed for a process for enhancing the rate of removal of water from deposition surfaces, deposition reactors, mass flow controllers, injectors, vacuum pumps and oil, and the like.